Intelligent Debris Removal Tool

ABSTRACT

A debris removal tool uses a screen to separate the debris coming into the tool from the moving fluid. The fluid that gets through the screen then operates a flow sensing device that is preferably a turbine whose speed of rotation or other characteristics of its movement generates a signal that is picked up by the measurement while drilling tool and conveyed to the surface. The surface personnel first respond by turning off surface pumps to allow debris to fall by gravity off the clogged screen. If that fails, the tool is pulled through the well fluid inducing a reverse flow through the screen to get the debris blocking it to go back into the well through the debris removal tool inlet.

FIELD OF THE INVENTION

The field of this invention is tools that can remove debris from a subterranean formation and provide feedback as to their operation to allow steps to be taken to improve debris removal efficiency without removal of the tool to the surface.

BACKGROUND OF THE INVENTION

When a metal object, such as a section of casing, a packer, or a lost tool, is to be removed from a well bore, the best method of removal is often to mill the object into small cuttings with a mill such as a pilot mill, a section mill, or a junk mill, and then to remove the cuttings from the well bore. Furthermore, a milling tool will often result in the removal of scale, cement, or formation debris from a hole. Also during completion phases of multi zone wells packer plugs are set on top of packers and sand is dumped on top of the plug to protect it from debris. The well is perforated and formation sand and perforation and gun debris will settle out on top of the sand. The amount of this sand and debris that is produced after perforating is unknown and therefore making the need for a flow indicator that much more important to know when the flow stops or the tool is full.

It is important to remove the cuttings, or other debris, because other equipment subsequently used in the well bore may incorporate sealing surfaces or elastomers, which could be damaged by loose metal cuttings being left in the hole. Most commonly, the metal cuttings and other debris created by milling are removed from the well bore by circulating fluid down the inside of the workstring and out openings in the milling tool, then up the annulus to the surface of the well site. This “forward circulation” method usually leaves some cuttings or debris stuck to the side of the well casing or well bore surface, and these cuttings or debris can damage some of the tools which may subsequently be run into the hole. Also, safety devices such as blow-out preventers usually have numerous cavities and crevices in which the cuttings can become stuck, thereby detracting from the performance of the device or possibly even preventing its operation. Removal and clean-out of such safety devices can be extremely expensive, often costing a quarter of a million dollars or more in the case of a deep sea rig. Further, rapid flow of debris-laden fluid through the casing can even damage the casing surface. Nevertheless, in applications where a large amount of metal must be removed, it is usually necessary to mill at a relatively fast rate, such as 15 to 30 feet of casing per hour. These applications call for the generation of relatively large cuttings, and these cuttings must be removed by the aforementioned method of “forward circulation”, carrying the metal cuttings up to the well site surface via the annulus.

In some applications, such as preparation for the drilling of multiple lateral well bores from a central well bore, it is only necessary to remove a relatively short length of casing from the central bore, in the range of 5 to 30 feet. In these applications, the milling can be done at a relatively slow rate, generating a somewhat limited amount of relatively small cuttings. In these applications where a relatively small amount of relatively small cuttings are generated, it is possible to consider removal of the cuttings by trapping them within the bottom hole assembly, followed by pulling the bottom hole assembly after completion of the milling operation. The advantage of doing so is that the cuttings are prevented from becoming stuck in the well bore or in a blow-out preventer, so the risk of damage to equipment is avoided.

Some equipment, such as the Baker Oil Tools combination ball type Jet and junk basket, product number 130-97, rely upon reverse circulation to draw large pieces of junk into a downhole junk removal tool. This product has a series of movable fingers which are deflected by the junk brought into the basket, and which then catch the larger pieces of junk. An eductor jet induces flow into the bottom of the junk basket. This tool is typical, in that it is generally designed to catch larger pieces of junk which have been left in the hole. It is not effective at removing small debris, because it will generally allow small debris to pass back out through the basket.

Moreover, the ability of this tool to pick up debris is limited by the fluid flow rate which can be achieved through the workstring, from a pump at the well site. In applications where the tool must first pass through a restricted diameter bore, to subsequently operate in a larger diameter bore, the effectiveness of the tool is severely limited by the available fluid flow rate. Additionally, if circulation is stopped, small debris can settle behind the deflecting fingers, thus preventing them from opening all the way. Further, if this tool were to be run into a hole to remove small cuttings after a milling operation, the small cuttings would have settled to the bottom of the hole, making their removal more difficult. In fact, this tool is provided with coring blades for coring into the bottom of the hole, in order to pick up items which have settled to the bottom of the hole.

Another type of such product is the combination of a Baker Oil Tools jet bushing, product number 130-96, and an internal boot basket, product number 130-21 which uses a jet action to induce fluid flow into the tool laden with small debris. The internal boot basket creates a circuitous path for the fluid, causing the debris to drop out and get caught on internal plates. An internal screen is also provided to further strip debris from the fluid exiting the tool. The exiting fluid is drawn by the jet back into the annulus surrounding the tool. However, here as before, if this tool were to be run into a hole to remove small cuttings after a milling operation, the small cuttings would have settled to the bottom of the hole, making their removal more difficult. Furthermore, here again, the ability of this tool to pick up debris is limited by the fluid flow rate which can be achieved through the workstring.

Another known design is represented by a tool which employs a packoff cup seal to close off the wellbore between fluid supply exit ports and return fluid exit ports. A reverse circulating flow is created by fluid supply exit ports introducing fluid into the annulus below the packoff cup seal, which causes fluid flow into the bottom of an attached milling or washover tool. This brings fluid laden with debris into the central bore of the reverse circulating tool, to be trapped within the body of the tool. The reverse circulating fluid exits the body of the tool through return fluid exit ports above the packoff cup seal and flows to the surface of the well site via the annulus. This tool relies upon the separation of the supply fluid and the return fluid, by use of the packoff cup seal between the fluid supply exit ports and return fluid exit ports. To avoid damage to this cup during rotation of the tool, the packoff cup seal must be built on a bearing assembly, adding significantly to the cost of the tool. Additionally, here as before, the ability of this tool to pick up debris is limited by the fluid flow rate which can be achieved through the workstring.

Milling downhole components generates debris that needs to be removed from circulating fluid. Fluid circulation systems featuring flow in different directions have been tried. One design involves reverse circulation where the clean fluid comes down a surrounding annulus to a mill and goes through rather large ports in the mill to take the developed cuttings into the mill to a cuttings separator such as the VACS tool sold by Baker Oil Tools. Tools like the VACS cannot be used above a mud motor that drives the mill and can only be used below a mud motor when using a rotary shoe. Apart from these limitations the mill design that requires large debris return passages that are centrally located forces the cutting structure to be mainly at the outer periphery and limits the application of such a system to specific applications. This tool is illustrated in U.S. Pat. No. 6,276,452.

The more common system involves pumping fluid through a mandrel in the cuttings catcher so that it can go down to the mill and return up the surrounding annular space to a discrete passage in the debris catcher. Usually there is an exterior diverter that directs the debris laden flow into the removal tool. These designs typically had valves of various types to keep the debris in the tool if circulation were stopped. These valves were problem areas because captured debris passing through would at times cling to the valve member either holding it open or closed. The designs incorporated a screen to remove fine cuttings but the screen was placed on the exterior of the tool putting it in harm's way during handling at the surface or while running it into position downhole. These designs focused on making the mandrel the main structural member in the device which resulted in limiting the cross-sectional area and the volume available to catch and store debris. This feature made these devices more prone to fill before the milling was finished. In the prior designs, despite the existence of a screen in the flow stream through the tool, some fines would get through and collect in the surrounding annulus. The fixed debris barriers could get stuck when the tool was being removed. In some designs the solution was to removably mount the debris barrier to the tool housing or to let the debris barrier shift to open a bypass. In the prior designs that used cup seals looking uphole for example, if the screen in the tool plugged as the tool was removed the well could experience a vacuum or swabbing if a bypass around the cup seal were not to open.

Typical of the latter type of designs is U.S. Pat. No. 6,250,387. It accepts debris in FIG. 3 at 11 and all the debris has to clear the ball 12 that acts as a one way valve to retain debris if the circulation is stopped. Debris plugs this valve. The screen 6 is on the tool exterior and is subject to damage in handling at the surface or running it into the well. That screen filters fluid entering at 7 as the tool is removed. It has an emergency bypass 20 if the screen 6 clogs during removal operations. It relies on a large mandrel having a passage 3 which limits the volume available for capturing debris. By design, the cup 5 is always extended.

U.S. Pat. No. 7,188,675 again has a large mandrel passage 305 and takes debris laden fluid in at 301 at the bottom of FIG. 4. It uses internal pivoting valve members 203 shown closed in FIG. 5a and open in FIG. 5b. These valves can foul with debris. It has an exterior screen 303 than can be damaged during handling or running in. Its diverter 330 is fixed.

Finally U.S. Pat. No. 6,776,231 has externally exposed screen material 4 and a debris valve 20 shown in FIG. 3 that can clog with debris. It does show a retractable barrier 9 that requires a support for a part of the tool 7 in the wellbore and setting down weight. However, this barrier when in contact with casing has passages to try to pass debris laden flow and these passages can clog.

Well cleanup tools with barriers that function when movement is in one direction and separate when the tool is moved in the opposite direction are shown in Palmer US Application 2008/0029263. Other articulated barriers are illustrated in U.S. Pat. No. 6,607,031 using set down weight and U.S. Pat. No. 7,322,408 using an inflatable and a pressure actuated shifting sleeve that uncovers a compressed ring to let it expand and become a diverter.

One of the issues with the Baker Hughes VACS tool that is illustrated in U.S. Pat. No. 6,276,452 is that if the screen plugs with debris there was really not any way for surface personnel to know that. What was simply happening is that flow would exit the tool laterally and would not flow down to the tool bottom to come back up through the tool bringing in more debris to be separated. Instead all the laterally exiting flow would simply go up the annulus to the surface as a part of it normally does during regular operation. From the surface, this difference is not discernable. The cause of this condition is a clogged screen with debris.

An attempt was made to address this problem of no surface feedback and the offered solution redesigned the tool described in U.S. Pat. No. 6,276,452 so that there was a way to detect a flow interruption or reduction that triggered various sleeves to move so that with the surface pumps remaining on the flow through the tool could temporarily reverse in an effort to get the debris off the screen so that it would be open to flow. In U.S. Pat. No. 7,472,745 a sensor for flow was described without detail as a way to trigger the flow reversal scheme in the tool to try to get its screen cleaned free of debris so that flow could resume when the passages were again reconfigured for regular operation. The issue here was that the sleeves that had to be actuated to reverse the flow to attempt to clean the screen also took up space and reduced the debris carrying capacity of the tool as well as presenting more moving parts that had an opportunity to fail. There were no details provided as to how to place a flow sensor where it would work most reliably and how that sensor would cope with abrupt reversals in pressurized flow direction.

The present invention presents a method of reliably sensing flow in a debris removal tool so that real time data is available at the surface and if there is a flow reduction detected then the method accomplishes unclogging the screen without additional components in the tool but rather relies on simpler techniques such as first shutting off the pumping equipment and if that still does not resolve the problem then pulling the tool up the hole approximately 300 to 1000 feet as to induce reverse flow through the screen and get the accumulated debris off of it followed by resuming normal operation. These and other aspects of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawing while recognizing that the full scope of the invention is given by the appended claims.

SUMMARY OF THE INVENTION

A debris removal tool uses a screen to separate the debris coming into the tool from the moving fluid. The fluid that gets through the screen then operates a flow sensing device that is preferably a turbine whose speed of rotation or other characteristics of its movement generates a signal that is picked up by the measurement while drilling tool and conveyed to the surface. The surface personnel first respond by turning off surface pumps to allow debris to fall by gravity off the clogged screen. If that fails, the tool is pulled through the well fluid inducing a reverse flow through the screen to get the debris blocking it to go back into the well through the debris removal tool inlet.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates the tool in the normal operation mode for removing debris at a screen.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic structure of the preferred design of the debris removal device is described in U.S. Pat. No. 6,276,452 and illustrated again in the FIGURE to provide a better understanding of the invention. In essence a tubular string to the surface is shown schematically as 10. There can be a mill at the base of the tool that is not shown but the arrows 12 are intended to illustrate flow entering the unshown mill and passing through an inlet tube 14 into a chamber 16 defined within the housing 18. The debris 20 hits the cap 22 its velocity slows in the space 16 so that it falls by its own weight into annular collection space 24. The fluid now without much of the larger debris as represented by arrows 25 hits the screen 27 which stops all but the very fine debris still carried by the flow stream which now exits the other side of the screen 27 as represented by arrows 26.

The filtered stream 26 next engages the flow measurement device 28 which in the preferred embodiment is a set of turbine blades that the passing flow engages and causes rotation about shaft 30. There is a sensor 32 on shaft 30 to sense the speed of the turbine 28 and send that data up a communication conduit 34 that communicates with a schematically represented measurement while drilling tool 36 of a type known in the art and that operates with flow that normally runs through it coming downhole as represented by arrows 38. Arrow 40 indicates that the flow or other signal that represents the flowing or non-flowing condition through the tool goes to the surface where surface personnel or processors can respond and take action as will be described below.

In normal operation the flow represented by arrows 38 enters an eductor 40 that has a discharge at 42 with a housing exit at 44. The flow rushing out the opening 44 induces a lower pressure above the turbine 28 and brings up flow as indicated by arrows 46 to the opening 44 to blend with the flow discharged from nozzle 42. During normal operation with the screen 27 open to flow, some of the flow to exit port 44 goes down as represented by arrow 47 to the mill (not shown) and comes into the debris removal tool as represented by arrow 12. The rest of the flow goes uphole as represented by arrow 48. Normally, the split is about one third of the flow in the direction of arrow 47 and two thirds going the way of arrow 48.

If the screen 27 clogs with debris 20 then what happens is that the circulation represented by arrow 47 falls off to nothing and that flow is redirected in the direction of arrow 48. The turbine 28 should recognize this condition and get a signal to the surface 40 through the measurement while drilling tool 36. When surface personnel or a processor on the surface recognizes this condition from the signal at arrow 40, a first step that can be taken is to clear the screen 27 by turning off the surface pump which has the effect of shutting off flow represented by arrows 38. It may happen that just shutting off the flow will allow debris 20 that is on the outer surface 50 of the screen 27 to simply fall off due to its own weight and land in annular space 24.

If shutting the circulation by eliminating flow represented by arrows 38 does not work as can be quickly determined by simply firing up the surface pumps to see if the turbine 28 registers any flow, then a next step is to pick up the tool housing 18 with the string 10. When that happens, flow will be induced in the tool in the direction of arrows 38. That flow can go in two ways and will follow the path of least resistance. In one direction it has to get through the nozzle 42 which is designed for pressurized flow to drop most of its pressure at the nozzle discharge so as to induce a lower pressure and flow represented by arrows 46, as previously discussed. This is the relatively high resistance flow path which means that most of the flow will be channeled against the inside surface 52 of the screen 27 and will act to push the debris 20 off the screen 27 and clear it up so that flow can resume when the surface pumps are later turned on and flow represented by arrow 38 starts again. The turbine 28 then gives feedback on whether the screen has been cleared. The order of operation can be reversed so that the tool can be picked up before the surface pump is cut off although the preferred order is turning off the surface pumps and determining if that resolved the problem before moving the tool uphole with the pump at the surface in the off position. The two operations can also be done at the same time.

While the invention has been described in the context of using a turbine 28 as the flow meter other sensors that can report on the amount of flow are envisioned to be substitutes. For example vibration induced by flow can be measured and correlated to flow as schematically illustrated by sensor 32. A mill is not needed as the tool by itself can be run in to remove debris already in the well. If a mill is to be used it is preferred for this style of a debris removal tool that the flow into the mill be in reverse flow mode so that the debris laden cuttings go into the mill and then right into the tube 14 for removal in the manner described above. While the preferred debris removal tool has been described as shown in the FIGURE the method of the present invention is adaptable to other styles of debris removal tool if they are configured to clear a screen by stopping circulation or pulling out of the hole. The flow signal can come to the surface through a hard wire connection or in other ways and does not necessarily need to go through a measurement while drilling device. The signal can be sent acoustically or on a fiber optic cable as a few examples of signal transmission with or without wire or cable.

Those skilled in the art will appreciate that as compared to U.S. Pat. No. 7,472,745 various sleeves and drivers for them can be eliminated leaving more room for flow and debris accumulation. While pump power is not employed to clear a screen, the resulting tool is left more simple in construction so that it can have a greater debris removal capacity with options for clearing a screen 27 in the even a low or no flow condition is detected. The flow sensor whether measuring flow directly or indirectly can have redundancy so that if one sensor malfunctions there can be a backup that can be selected to be able to continue to get feedback.

The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below. 

1. A method of operating a debris removal tool in a wellbore comprising: moving fluid downhole to direct debris into a downhole debris catcher; separating debris from said moving fluid with a screen; sensing a change in flow through said debris catcher; getting a signal at a surface location regarding said change in flow; stopping fluid movement through said debris catcher in response to said signal.
 2. The method of claim 1, comprising: pulling said debris catcher uphole.
 3. The method of claim 2, comprising: pulling said debris catcher uphole after stopping said fluid movement.
 4. The method of claim 2, comprising: pulling said debris catcher uphole before stopping said fluid movement.
 5. The method of claim 1, comprising: sensing flow with a turbine flow sensor.
 6. The method of claim 1, comprising: sensing flow indirectly by measuring a parameter different than flow.
 7. The method of claim 6, comprising: measuring vibration as a way of determining flow.
 8. The method of claim 1, comprising: sensing flow downstream of said screen.
 9. The method of claim 8, comprising: placing a flow sensing device between said screen and an eductor that draws fluid through said screen.
 10. The method of claim 1, comprising: sending a signal from a flow sensor is said debris catcher to a measurement while drilling device; relaying a signal from said measurement while drilling device to the surface.
 11. The method of claim 10, comprising: manually turning off a pump that moves fluid in said debris catcher in response to a predetermined change in said relayed signal.
 12. The method of claim 10, comprising: using a controller at the surface to automatically turn off a surface pump that moves fluid in said debris catcher in response to a predetermined change in said relayed signal.
 13. The method of claim 1, comprising: positioning said screen over a debris storage volume in said debris catcher; allowing debris on said screen to fall into said volume when pumped fluid movement through said debris catcher is stopped.
 14. The method of claim 13, comprising: picking up said debris catcher after said stopping of said fluid movement through said debris catcher.
 15. The method of claim 13, comprising: picking up said debris catcher before said stopping of said fluid movement through said debris catcher.
 16. The method of claim 13, comprising: picking up said debris catcher at the same time as said stopping of said fluid movement through said debris catcher. 